Quite a lot. Because the real question is: What can go right for Trump?

Start with the Democrats’ structural problem. In the House, gerrymandering and demographic sorting protect the GOP. By expert consensus, only 35 to 40 of 435 House seats are competitive. As of now, Republicans hold 239; the Democrats 193. To capture the House, the Democrats need 218 — a gain of 25.

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The Senate is even harder. Each state gets two seats, regardless of population — because of demographic sorting, more states are red than blue.

Republicans now hold a 51-49 majority. Of the 34 seats being contested in 2018, the Democrats are defending 26 — including two independents. The GOP is defending a mere eight: only three — Nevada, Oregon, and Tennessee — seem vulnerable. But three Democratic seats — North Dakota, Missouri, Indiana — are shaky. If these are the seats in play, Democrats must run the table to win control.

Granted, Trump’s current weaknesses could undermine the GOP’s impressive electoral fortifications. But public opinion is seldom static. The general distaste for Trump persists despite a decline in unemployment and a rising stock market — in which many Americans now have a stake. By November, more voters may be inclined — reasonably or not — to give Trump credit.

Almost inevitably, his tax law will become somewhat more popular. In the next few months, many Americans will get a modest bump in take-home pay: the law’s more regressive effects, and its potential to explode the deficit, won’t become politically salient until later.

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If the overall economy stays relatively benign, as many economists expect, Trump will tout his tax measure as an indispensable component of prosperity. Thus the Democrats’ most universal talking point, economic equity, may lose resonance. Much the same is true of the GOP attack on Obamacare — the worst consequences will be most widely felt after 2018.

Other key components of the political zeitgeist — polarization and a general distrust of both parties — could also benefit Trump. If he floats a more bipartisan agenda — infrastructure being the most obvious — Democrats must decide whether to cooperate or, for ideological and political reasons, oppose.

The Republican version of infrastructure spending may be short on federal dollars, and long on tax credits, frustrating Democratic hopes for a substantial upfront investment. Moreover, the party’s base voters are bitterly opposed to cooperation with Trump. Thus the chances of bipartisan agreement appear dim.

In the case of no compromise, Trump could benefit by complaining that Democrats frustrated his efforts to rebuild America. With respect to more volatile issues, such as restoring DACA or the Child Health Insurance Program, Republicans will seek to take these off the table — or blame Democrats should their efforts fail.

Here Republicans may founder, strapped to a leader many Americans find exhausting. But many voters find fatigue more numbing than infuriating. If their lives seem good enough, familiarity may breed passivity.

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True, Democrats have the passion; in typical off-year elections, turnout rules. But by exclusively focusing on Trump, they risk personifying hysteria untethered to a positive vision. A party so disconnected from power has no persuasive national spokesperson or program, and impotent preelection threats of impeachment could drive Trump’s loyalists to the polls. Trump may have to outdo himself to reanimate mass horror.

Nuclear peril could suffice, or a catastrophic land war on the Korean Peninsula. The Mueller investigation could expose Trump as a knowing pawn of Russia or, more immediately, a president so desperate to avoid exposure that he provokes a constitutional crisis. If one credits the considerable evidence that Trump colluded with Russia, obstructed justice — or both — that seems likely.

But no sane political party expects such things. Nor should it rely on loathing and litmus tests directed solely at the most committed.

Democrats need to offer average Americans a positive vision for their lives, choosing strong issue-driven candidates who can win close contests while building for the future by reaching more voters across the country. Unless they do, the Democrats should prepare themselves for a bitter electoral reprise in 2018 — Donald Trump filling their screens as he proclaims yet another “historic” victory.

Richard North Patterson’s column appears regularly in the Globe. His latest book is “Fever Swamp.” Follow him on Twitter @RicPatterson.